1. Field of the Invention
The present invention relates to a polyoxyalkylene monoalkyl ether, a process for producing the polyoxyalkylene monoalkyl ether, a polymerizable polyoxyalkylene monoalkyl ether derivative, a polymer of the derivative and a dispersant comprising the polymer. More particularly, the present invention relates to a high purity polyoxyalkylene monoalkyl ether which does not contain bifunctional alcohol compounds, a process for producing the polyoxyalkylene monoalkyl ether, a polymerizable polyoxyalkylene monoalkyl ether derivative prepared by using the polyoxyalkylene monoalkyl ether as a raw material, a polymer of the derivative, and a dispersant comprising the polymer and having an excellent dispersing property.
2. Description of the Related Arts
Polymerizable polyoxyalkylene monoalkyl ether derivatives have recently been developed and polymers and copolymers prepared from these derivatives used as monomers and other monomers have also been developed. However, the polymers and the copolymers prepared from such polyoxyalkylene monoalkyl ethers used as monomers occasionally do not exhibit the properties expected from the polymers and the copolymers because of a distribution of molecular weight broader than expected or formation of gel during polymerization. One of the reasons why these undesirable phenomena take place is considered to be the crosslinking reaction of bifunctional polyoxyalkylene glycol derivatives contained in the polymerizable polyoxyalkylene monoalkyl ether derivatives as byproducts.
To overcome the above problem, a polymerizable polyoxyalkylene monoalkyl ether derivative which does not contain any bifunctional polyoxyalkylene glycol derivatives as byproducts can be used as the monomer. A polymerizable polyoxyalkylene monoalkyl ether derivative may be obtained, for example, by using a compound which has a polymerizable functional group and to which an alkylene oxide can be added as a raw material. In this case, the polymerizable polyoxyalkylene monoalkyl ether derivative of the object compound can be obtained by adding an alkylene oxide to the above compound and reacting an alkyl compound with the formed terminal hydroxyl group. However, side reactions such as rearrangement of the polymerizable functional group and polymerization of the compound having a polymerizable function group tend to take place in the reaction condition for addition of the alkylene oxide to the compound having a polymerizable functional group. Side reactions such as polymerization and decomposition of ester portions tend to take place in the reaction condition for forming an alkyl ether. As the result, compounds different from the object compound are frequently obtained. Therefore, to obtain a polymerizable polyoxyalkylene monoalkyl ether derivative, it is generally conducted that a polymerizable functional group is incorporated into a polyoxyalkylene monoalkyl ether.
A bifunctional polymerizable polyoxyalkylene glycol derivative which is formed in the preparation of a polymerizable polyoxyalkylene monoalkyl ether derivative as a byproduct is derived from a polyoxyalkylene glycol contained as a byproduct in a polyoxyalkylene monoalkyl ether used as a raw material of the polymerizable polyoxyalkylene monoalkyl ether derivative. In other words, when the polymerizable functional group is incorporated into a polyoxyalkylene monoalkyl ether using, as the raw material, a polyoxyalkylene monoalkyl ether containing a polyoxyalkylene glycol as a byproduct, a polymerizable polyoxyalkylene glycol derivative having two polymerizable functional groups at the both end portions corresponding to the portions of the hydroxyl group in the polyoxyalkylene glycol is formed as a byproduct along with the monofunctional polymerizable polyoxyalkylene monoalkyl ether derivative of the object compound because the polymerizable functional group is incorporated into the portion of the hydroxyl group. Therefore, a polymerizable polyoxyalkylene monoalkyl ether derivative which does not contain any polymerizable polyoxyalkylene glycol derivatives having two polymerizable functional groups can be obtained when the used polyoxyalkylene monoalkyl ether does not contain any polyoxyalkylene glycols as byproducts.
A polyoxyalkylene monoalkyl ether is produced by direct addition of an alkylene oxide to a monohydric alcohol used as a raw material in the presence of an alkali catalyst or an acid catalyst. It is known that a plurality of byproducts are formed in this reaction depending on the condition of production (Yoshihiko Oshima and Toshiyasu Mizutani, Toso Kogaku (Coating Engineering), Volume 22, Pages 397 to 403, 1987). For example, when an alkylene oxide is added to a monohydric alcohol using a hydroxide of an alkali metal or an alkaline earth metal as the catalyst or when an alkylene oxide is added to a monohydric alcohol in the condition that water is present in a reactor, water and the alkylene oxide react to form a bifunctional glycol and further addition of the alkylene oxide to the formed bifunctional glycol takes place. As the result, polyoxyalkylene glycols which are dihydric alcohol compounds are formed as byproducts along with a polyoxyalkylene monoalkyl ether which is a monohydric alcohol compound. It is not easy to selectively separate a polyoxyalkylene monoalkyl ether from a mixture of the polyoxyalkylene monoalkyl ether and byproducts. The separation of the materials in large amounts is particularly difficult. Moreover, it is often difficult to determine the content of polyoxyalkylene glycols in a mixture with a polyoxyalkylene monoalkyl ether. Therefore, it is often difficult to decide whether an available polyoxyalkylene monoalkyl ether is suitable as the raw material for a polymerizable polyoxyalkylene monoalkyl ether derivative or not. Naturally, it is also difficult to determine the content of bifunctional polymerizable polyoxyalkylene glycol derivatives in a polymerizable polyoxyalkylene monoalkyl ether derivative obtained by using the above ether as the raw material.